Well, as a source for metadata or covers it's okay, as long as I don't have to create an account. I don't see the need for a read books- feature from Goodreads, as it's easily done with what Calibre provides now: Just create a custom boolean column.

This is along the lines of what I was thinking. A source of metadata and custom category information. The possibility exists to synchronize the two, as well.

There really isn't room in Calibre for the social aspects of Goodreads.